package com.example.performance.jmh.official;

import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

/**
 * Since @State objects are kept around during the lifetime of the benchmark,
 * it helps to have the methods which do state housekeeping.
 * These are usual fixture methods, you are probably familiar with them from JUnit and TestNG.
 * <p>
 * Fixture methods make sense only on @State objects,
 * and JMH will fail to compile the test otherwise.
 * <p>
 * As with the State, fixture methods are only called by those benchmark threads which are using the state.
 * That means you can operate in the thread-local context,
 * and (not) use synchronization as if you are executing in the context of benchmark thread.
 * <p>
 * Note:
 * fixture methods can also work with static fields,
 * although the semantics of these operations fall back out of State scope,
 * and obey usual Java rules (i.e. one static field per class).
 */
@State(Scope.Thread)
@SuppressWarnings("java:S101")
public class JMHSample_05_StateFixtures {

    double x;

    /**
     * Ok, let's prepare our benchmark:
     */
    @Setup
    public void prepare() {
        x = Math.PI;
    }

    /**
     * And, check the benchmark went fine afterwards:
     */
    @TearDown
    public void check() {
        assert x > Math.PI : "Nothing changed?";
    }

    /**
     * This method obviously does the right thing, incrementing the field x in the benchmark state.
     * check() will never fail this way,
     * because we are always guaranteed to have at least one benchmark call.
     */
    //@Benchmark
    public void measureRight() {
        x++;
    }

    /**
     * This method, however, will fail the check(),
     * because we deliberately have the "typo", and increment only the local variable.
     * This should not pass the check, and JMH will fail the run.
     */
    @Benchmark
    @Warmup(iterations = 2, time = 1)
    @Measurement(iterations = 2, time = 1)
    public void measureWrong() {
        double x = 0;
        x++;
    }

    /**
     * ============================== HOW TO RUN THIS TEST: ====================================
     * <p>
     * You can see measureRight() yields the result,
     * and measureWrong() fires the assert at the end of the run.
     * <p>
     * You can run this test:
     * <p>
     * a) Via the command line:
     *    $ mvn clean install
     *    $ java -ea -jar target/benchmarks.jar JMHSample_05 -f 1
     *    (we requested single fork; there are also other options, see -h)
     * <p>
     * b) Via the Java API:
     *    (see the JMH homepage for possible caveats when running from IDE:
     *      <a href="http://openjdk.java.net/projects/code-tools/jmh/">...</a>)
     */
    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(JMHSample_05_StateFixtures.class.getSimpleName())
                .forks(1)
                .jvmArgs("-ea")
                .build();

        new Runner(opt).run();
    }

}